1. Field of Invention
The present invention relates to simplified pressure regulation systems and more particularly to systems adapted to regulate the pressure of liquid discharge of a plurality of parallel liquid supply systems, e.g. the pressure of ink flow to a plurality of continuous ink jet printing heads.
2. Description of Background Art
In continuous ink jet printing apparatus which utilize a single print head, ink is pumped through a supply line from a supply reservoir to a print head, under sufficient pressure to cause ink streams to issue from the orifices of the print head. Stimulating vibrations are applied to the print head to cause those ink streams to form streams of uniformly sized and spaced droplets, which are electrically controlled into printing or non-printing paths. The non-printing droplets are returned to the supply reservoir via a droplet catcher and a return line. Usually there is a main return line which extends from a print head outlet to the ink reservoir to allow ink from the supply line to circulate through the print head, e.g. during start-up. Proper drop stream stimulation, as well as synchronization of droplet charging depend, in part, on maintaining a predetermined fluid pressure in the ink supplied to the print head.
Continuous ink jet printing systems have been proposed wherein a plurality of discrete orifice arrays cooperate in printing on a common print medium, e.g. to allow the use of different ink colors or to increase printing speed and/or printing resolution. These multi-head systems may or may not have separate ink reservoirs; however, in general, they utilize separate and completely duplicative ink circulation systems for each separate print head. Thus, each circulation system has its own separate pump motor and its own discrete system for regulating its print head ink pressure. Clearly it would be desirable from the viewpoints of cost, simplicity, apparatus size and reliability to reduce such duplication of components.
From the printing performance veiwpoint, the approach utilizing a plurality of completely separate ink circulation systems can operate successfully with slightly differing print head pressures by employing, for each print head, a servo system that cooperatively adjusts print head pressure and stimulation amplitude to: (i) avoid satellite droplets and (ii) achieve the proper filament break-off position. However, where a common stimulator operates on a plurality of print heads, the cooperative adjustment technique is not available, and it becomes very important for the print heads' ink pressures to be precisely the same. Also, when applying ink droplets from a plurality of print heads to a common substrate, drop placement accuracy requires equal print head droplet velocities, which in turn depends on equal ink supply pressures to the print heads. Thus, it can be seen that there are various printing performance needs for attaining the same nominal ink pressures for cooperative print heads. Attainment of such equal ink pressures in independent circulation systems having their own dedicated pressure regulation subsystems requires expensive calibration of each of the transducer/pump sets of the separate ink circulation systems.